By using duff's solution with the Matching the word boundary \b so that you don't chop off the text in the middle of a word.

update:
A clumsy other way to do this :)

use strict;
use warnings;
my $txt = "just wondering how i can have perl display part of my long +memo. basically i want the first lets say 255 charachters of the para+graph. im really new to perl so i don't know how i would come about t+his? a regex perhaps? just started reading about that today. so basic+ally something like";
my @a = split("",$txt);
my $l = 7;
for (my $i=0; $i < $l; $i++) {
print $a[$i];
$l++ if ($i ==($l-1) && ($a[$i] ne " " )) ;
}